1. Field of the Invention
The present invention relates to a rodless cylinder having a cylinder tube provided with an internal moving body disposed in the cylinder tube and moving along the axis of the tube and an external moving body disposed outside the cylinder tube and driven by the internal moving body through an axially extending slit formed on the wall of the cylinder tube. More specifically, the present invention relates to an inner seal band, disposed inside the cylinder tube, which seals the inner opening of the slit on the cylinder wall.
2. Description of the Related Art
A rodless cylinder which has an external moving body moving axially within a cylinder tube and an external moving body driven by the internal moving body through an axially extending slit on the wall of the cylinder tube is known in the art. A rodless cylinder of this type uses an inner seal band disposed inside the cylinder tube and extending along the slit on the cylinder wall in order to seal the inner opening of the slit. In some types of rodless cylinders, inner seal bands having flat faces on both sides are used.
Rodless cylinders using inner seal bands having flat faces are disclosed in various publications.
For example;
(A) Japanese Unexamined Utility Model Publication (Kokai) No. 62-81702, U.S. Pat. No. 3,820,446 and Japanese Unexamined Patent Publication (Kokai) No. 11-13711 disclose rodless cylinders having inner seal bands in the form of a flat metal band. In these publications, the inner seal band of the rodless cylinder is fixed to end members at both ends of the inner seal band. The end members (for example, end caps) are disposed at both ends of the cylinder tube of the rodless cylinder in order to close the open ends of the cylinder tube. The transverse movement of the inner seal band (the movement in the direction of the width of the inner seal band) is restricted by the connection with the end members at both ends of the inner seal band. At the portion between both ends, the inner seal band passes through a band guide recess formed on the internal moving body in the axial direction. However, in these publications, relatively large transverse clearances are formed between both side walls of the recess and the side edges of the inner seal band. PA1 (B) U.S. Pat. No. 3,893,378 discloses a rodless cylinder having an inner seal band which has flat faces. However, the inner seal band in this publication has a width substantially the same as the width of the band guide recess of the internal moving body. In this publication, since both side edges directly contact the side walls of the band guide recess, the transverse movement of the inner seal band is restricted by the band guide recess. PA1 (C) On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 7-259807 and Japanese Patent No. 2512354 disclose inner seal bands of different type. The inner seal bands in these publications have a cross-section shape which allows the inner seal band to fit into the slit of the cylinder tube wall or fitting grooves running parallel to the slit. Therefore, the transverse movement of the inner seal band is restricted along the entire length thereof.
Though the displacement of the inner seal band relative to the slit in the transverse direction hardly occurs in the publications (C), the inner seal bands having flat faces (i.e., the inner seal bands having a flat rectangular cross section shape) such as those disclosed in the publications (A) and (B) are liable to displace in the transverse direction with regard to the slit.
For example, the seal band in the publication (A) is restricted at both ends thereof in the transverse direction. However, since relatively large clearances remain between the side edges and the side walls of the band guide recess of the internal moving body, the middle portion of the inner seal band is not sufficiently restricted in the transverse direction. Therefore, the inner seal band tends to displace in the direction transverse to the slit. Especially, this is true when the stroke of the rodless cylinder is long, or the rodless cylinder is placed in the position where the slit faces a horizontal direction (i.e., when the width of the faces of the inner seal band is oriented to the vertical direction).
When the inner seal band shifts in the transverse direction relative to the slit of the cylinder tube, the seal performance of the inner seal band deteriorates and pressure fluid in the cylinder tube leaks from the slit. This causes so-called "stick and slip phenomena" of the rodless cylinder in which jagged movements of the inner and external moving bodies occur.
On the other hand, even though it uses the inner seal band having flat faces, the transverse displacement of the inner seal band is not likely occur in the rodless cylinders in the publications (B) since the transverse movement of the middle portion of the inner seal band is restricted by the contacts between the side edges of the inner seal band and the side walls of the band guide recess of the internal moving body. However, in the publication (B), the inner seal band is guided by the direct contact between the side edges of the inner seal band and the side walls of the seal band guide recess. Therefore, the width of the seal band must exactly match the width of the seal band guide recess of the internal moving body. This requires precise machining of the inner seal band and the side walls of the recess. Further, since the inner seal band and the side walls of the recess of the seal band guide directly contact each other, the problems of abrasion may occur. Since the internal moving body is a solid one-piece construction, it is difficult to use an abrasion resistant material only for the side walls of the recess. Further, if a material such as aluminum or steel is used for the internal moving body, dust is generated by the wear of the side walls and the seal band. In this case, dust generated by the wear attaches to the surface of the seal band. This causes deterioration of seal performance of the seal band and a shortening of the service life of the seal band.
Though the problems related to the transverse displacement of the inner seal band do not occur in the inner seal band of the publication (C), the cross section shape of the inner seal band and the slit or the guide grooves must be precisely machined. This requires an additional machining cost.